This invention relates to magnetic tape head assemblies for use in conjunction with magnetic recording tape.
Magnetic tape head assemblies typically contain one or more raised strips or "islands" over which the magnetic recording tape passes. Embedded in each island is a transducer, which may be an encoding element for writing information onto the tape, or a decoding element for reading information off of the tape. An encoding element produces a magnetic field in the vicinity of a small gap in the encoding element, which causes information to be stored on the magnetic recording tape as the tape streams over the island in contact with the island. Likewise, a decoding element detects a magnetic field near the surface of the tape as the tape streams over the island in contact with the island. Yet, there is typically some microscopic separation between the transducer and the recording tape that reduces the magnetic field strength detected by the tape or the decoding element. The reduction in the detected magnetic field strength is known as "spacing loss."
The magnetic field strength detected by the tape or the decoding element is proportional to e.sup.-kd/.lambda., where d is the head-to-tape separation, .lambda. is the recording wavelength, and k is a constant. The detected magnetic field strength decreases exponentially both with respect to separation between the tape and the island and with respect to recording density (which is inversely related to the recording wavelength .lambda.). Thus, while a limited amount of head-to-tape separation might be acceptable at low recording densities of 10-20 KFCI, at the higher densities (40-60 KFCI) of new, smaller transducers the head-to-tape separation must not exceed a few micro-inches.
When a uniform tension T is applied to a recording tape as the tape passes at a wrap angle .theta. around an island having a uniform height I.sub.H and a uniform width I.sub.w, the tape exerts a pressure P against the island that is uniform along an axis down the center of the length of the island. The pressure P is essentially proportional to the tension T and the wrap angle .theta. and inversely proportional to the island width I.sub.w. The pressure P of the tape against the island can be increased by increasing T or .theta., or by decreasing I.sub.w, thereby reducing any microscopic separation between the tape and the encoding element, and hence reducing spacing loss. This increased pressure tends to cause the island to wear down more rapidly, however, resulting in a shortened head life. Moreover, the increased pressure may result in depressions in the island that also contribute to spacing loss, thus making spacing loss unavoidable.